tty: tty_driver: introduce TTY driver sub/types enums

Convert TTY_DRIVER_TYPE_*, and subtype macros to two enums:
tty_driver_type and tty_driver_subtype. This allows for easier
kernel-doc (later), grouping of these nicely, and proper checking.

The tty_driver's ::type and ::subtype now use these enums instead of
bare "short".

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20250317070046.24386-16-jirislaby@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>